1. Field of the Invention
The present invention relates to sealing materials, and particularly to a sealing agent composition for sealing ion transport membranes (ITM).
2. Description of the Related Art
Ion transport membranes (ITMs) have been identified as very promising materials for separating oxygen from air with nearly perfect selectivity. Such membranes can be used for systems that require an oxygen rich environment, like oxy-fuel power plants. The operational temperature for this oxygen separation process is from about 700-1100° C. depending on the material used to prepare the ITM. Sealing the membranes between the support tubes at such high temperatures is a critical issue. If the membrane is not sealed perfectly, the air from the surroundings will mix with the separated oxygen on the permeate side of the membrane.
During the initial years of the ITM technology, many researchers tried to seal the ceramic membranes between metallic support tubes by brazing. Standard reactive metal brazing technology using titanium as an active element, however, requires high vacuum at high temperatures during brazing. These conditions destroy the required crystal structure in the membranes. Other known solutions include reactive air brazing (RAB) based on Ag—CuO brazes, which is performed in atmospheric air instead of a high vacuum. The bond thus formed becomes a permanent one upon cooling. Support tubes can be made from ceramic materials like alumina or quartz instead of a metal due to high operating temperatures.
Several researchers have attempted to use glass in the form of rings or paste to seal the membrane/support tube setup. The setup seals when the glass melts to fill the gaps between the membrane and the tube. However, at temperatures above the melting point of the glass, the glass continues to flow which may result in a loss of sealing. Also glass may react at high temperature with the membrane causing the seal to break. It also tends to diffuse towards the center of the membrane from the edges which causes the effective area available for permeability to reduce and errors in the calculation of oxygen flux to occur.
Thus, an improved membrane sealing agent material solving the aforementioned problems is desired.